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Help Me Understand Input/Output Voltage Specs |
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patientot 
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Joined: 28 Nov 2018 Location: USA Status: Offline Points: 1525 |
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 Topic: Help Me Understand Input/Output Voltage SpecsPosted: 05 May 2019 at 9:42pm |
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My apologies if this has already been covered, but I am just
trying to understand how things work from the perspective of a layman
(non-engineer). I’m trying to understand the relationship between maximum
input voltage, cartridge output, overload margin, and peak output while playing
a record. From the Reflex M description: It's OK if your music is
quiet all the way, but music is dynamic and hits transient peaks. Recording
desk PPM meters red-line at +8dB (2.5 times the signal), but in reality the
signal overshoots to nearer +14dB which is 5 times bigger. Add the fact that magnetic cartridge output voltage rises in
proportion to frequency (they all do), and clearly-audible highs are going to
be +10dB higher than the cartridge's official 1kHz output rating. With peak
added-on the input is called on to accept nearly 80mV for the average 5mV
output cartridge. Now if the input must accept ~80mV on peaks with a 5mV cart
(and I assume more with a higher output cart), then how does that work with a maximum
input voltage of 46mV rms as stated in the spec? Likewise, if the max output is 5.2V rms,
then how does the input accept a range from 179mV to 1030mV? I know I must be missing something here – just trying to get
a better understanding of how things work. Edited by patientot - 05 May 2019 at 9:43pm |
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SL-1200 MK7 (modified) + Reflex M + PSU-1 used with AT150-40ML, AT VM95ML, Stanton 680mkII + Ogura, and Shure M35X cartridges.
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Graham Slee
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Retired Joined: 11 Jan 2008 Location: South Yorkshire Status: Offline Points: 16298 |
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Posted: 05 May 2019 at 10:47pm |
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What's missing is the understanding (or lack of) that the output of a magnetic cartridge is not flat (like the plots in another topic), and until the decievers or ignoramuses stop presenting the output of a magnetic cartridge driven phono equaliser as being the FR of the cartridge, confusion will remain. But with leaders like Fremer confusion is guaranteed to remain. It was hard for the US Patent office examiners to see it at first...
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Graham Slee
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Posted: 06 May 2019 at 7:05am |
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I'm quite happy to help anybody understand so long as it isn't a rhetorical question. According to the the Jewish historian Josephus, the Babylonian historian Berossus, and the Roman historian Eusebius, there was a bloke going round explaining that the earth was a sphere in orbit around the sun. It took mankind over 3000 years to realise he was right! He knew about it because he observed things. I also observe. I also had use of a record player equipped with a piezo-electric phono cartridge (a crystal cartridge), as well as three discotheque systems equipped with another type of piezo-electric phono cartridge: a ceramic cartridge. I will have to assume that none of the readers here did, and that none of the hi-fi reviewers did either. So here's the history lesson you have to understand before you have any chance of understanding the answer to your question. But first you have to be dragged away from the flat-earthers you believe in? However, cults somehow manage to persuade people otherwise, so I can't see many readers sticking with me over this. In this first simple lesson you need to understand the simple way the ceramic (or crystal) cartridges work, and here is an excerpt taken from National Semiconductors' Audio/Radio handbook, published as recently as 1980 (Fig.1):  So what did we learn from that? We found that the FR of the (RIAA) record is flat except for a 12dB drop in level between 500 Hz and 2122 Hz. But the cultish people always show it as this (Fig.2):  How come? Maybe they're snobs? That they never trod the lowly path of "cheap" ceramic and crystal cartridges? If they had they would realise how wrong they are. So, let's repeat the mantra "the output of the record is flat! - the output of the record is flat!" (except except for a 12dB drop in level between 500 Hz and 2122 Hz). The reason why Fig.2 is like it is, is because the output of a magnetic cartridge looks like this (Fig.3):  So how come you see magnetic cartridge plots showing flat FR? Because it has been "normalised" by somebodies RIAA phono stage! The next lesson will follow...
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Graham Slee
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Posted: 06 May 2019 at 8:11am |
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I remember the story of a postman delivering an LP record, but nobody was home, and it wouldn't go through the letter flap in the door...
So he folded it in half! OK. Question time. If a magnetic cartridge outputs 5mV at 1kHz what does it output at 100Hz and 10kHz... a. using a record with a flat FR? b. using a record with RIAA FR? Answers: a. 0.5mV and 50mV; b. 1.1mV and 24.2mV There is no flat FR record so answer a. is a misnomer. To do a flat FR record requires a 1,000:1 ratio between 20kHz and 20Hz, and like the postman found, it don't fit! What don't it fit? The dynamic range of the electronics! A ratio of 100:1 fits! RIAA folds the FR to make it fit. It's folded between 500Hz and 2122Hz by a factor of 4. And it's folded between 20Hz and 50Hz by a factor of 2.5. 2.5 x 4 = 10. 1,000 / 10 = 100. |
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Graham Slee
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Posted: 06 May 2019 at 8:17am |
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Do I get a response from class? Nobody left me a banana on my desk!
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Graham Slee
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Posted: 06 May 2019 at 8:35am |
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Oh well. Never mind. Class must be away today. It is after all a public holiday in the UK.
Instead I will indulge in a little history. The reason for it taking around 3000 years for science to catch-up with the bloke I mentioned earlier, was because of beliefs. You see, it went against the beliefs of the priests or preachers of the time, and they invented a word to describe the truth. It was called heresy, and the dictionary definition of heresy is: opinion profoundly at odds with what is generally accepted. So they accepted lies as being truth, and that the earth was flat, or that the sun orbited the earth, because that was generally accepted. And even today we have politicians who think the same way. So when millions of people vote to tell them to take a hike, they believe they voted to be stitched up. Life gets tee-jus don't it? |
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Lucabeer
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Posted: 06 May 2019 at 10:42am |
I guess this must be quite a trouble to design an MM stage, then. MM cartriges usually have a range of (declared) output between 2 and 8 mV @1KHz. This means that the range of inputs into the phono stage (taking RIAA equalization baked into the record) is somehow in the range between approximately 0.1 mV (2 mV cartridge @20Hz) and 78 mV (8 mV cartridge @20KHz), which is quite wide!
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